Titanium, as well as 24-carat gold and Niobium are wellknown for their hypo-allergenic qualities. They do not cause allergic reactions.
An allergic reaction is caused by exchange of ions with the skin. Nickel is infamous for doing this but even different types of plastic can cause irritation of the skin.
Titanium is accepted by the body as a non-alien substance.
In modern surgery titanium pins and screws are used to fix broken and shattered bones. Bone will actually grow onto the titanium.
Under normal circumstances it would be impossible to solder or weld titanium in a studio. Using high-tech from America I can point-weld pins behind the earrings.